Setscrew



Patented Mar. l, 1949 UNITED STATES ATENT OFFICE SETSCREW Leon E.Simmons, Claremont, N. H., assignor to Joy Manufacturing Company, acorporation of Pennsylvania 7 Claims.

My invention relates to set screws and more particularly to set screwsfor securing cutter bits or cutter bit holders in the chain blocks ofthe cutter chains of coal cutting machines.

Coal cutting machines, in this country, are practically universallyequipped with circulating (orbitally moving) cutter chains madeupvgenerally of bit-carrying blocks and connecting links. Thebit-carrying blocks have sockets in which the Shanks of resharpenablebits, or the holders of so-called throw-away type bits, are adapted tobe received; and set screws are provided to engage the Shanks of thebits or bit holders and clamp them in these sockets. The cuttinginstrumentalities are subjected to very powerful forces tending to causetheir loss, and there is, of course, much vibration which tends toloosen the set screws.

Conventional set screws are formed with their bitor bit holder-engagingends frusto-conically shaped externally, and countersunk so that anannular work-engaging portion generally V- shaped in radial section isprovided. Tightening of the set screws results in advance of the screwsat a rate determined by the lead of the screw threads, and the pressureexerted by the screw action forces the sharpened annular portions at thefront end of the screws into the metal of the bit or of the holdershank. There is no mechanical interlock, as distinguished from africtional holding effect, tending to prevent the backing out of thescrew. Of course, direct withdrawal of the bit or holder until the screwhas been slightly loosened will be prevented by the embedding of theforward end of the annular formation at the work-engaging end of thescrew; but, aside from the friction actionthe binding between thesurfaces of the threads and the threaded bore in which they are arrangedand the binding action of the surfaces at the inside and outside of theforemost annular edge of the screwthere is nothing to keep the bit frombeing loosened by reason of vibration.

According to my invention, there is secured a large part of thefrictional binding` action of conventional set screws, but there isadded to this the necessity of detaching or rolling down a chip formedas the set screw is turned homej and getting this chip out of the way asthe set screw is backed out, takes substantial force. In a preferredembodiment, I accomplish these results by retaining the externallyfrusto-conical, internally countersunk forward portion of the set screwthroughout the greater part of the circumference, and by providing,preferably at substantial diametrically opposite points, notches in thisforemost portion of the screw, in such manner that the leading edge orWall of each notch, in terms of the direction of rotation of the setscrew during tightening, slopes rearwardly, while the rearward wall, interms of the direction of tightening rotation, is desirably relativelynearly parallel to the axis of rotation of the screw. Thecircumferential dimension of the notch is determined with twoconsiderations in mind:

l. The desire to maintain at least the major part of the foremost end ofthe bit intact, and

2. The desire to provide for the formation of a chip or chips of thenecessary thickness.

It will be understood that, since the forward end of the set screwadvances as it rotates, the thickness of the chip raised as the screw isturned home depends on the circumferential dimension of these notches.The greater the circumferential dimension of the notch, the thicker thechip. Desirably, the width of the notch will be made sufficient to forma chip of sucient strength to effect the desired resistance to looseningof the screw, but only of sufcient thickness for that purpose, wherebythe set screw will not needlessly cut up the metal of the shank which itengages, and whereby a considerable part of the frictional holding ofthe conventional set screw will be retained, and whereby there may be anecessity for the leading, sloping wall of the notches to override thechips formed as far as possible instead of simply detaching them. Theabsence of relief behind the chip raising surfaces will provide formaximum frictional holding of the screw and also result in chips ofmaximum strength and in maximum Xity, so to speak, of the chips to thebody with which they are attached.

The depth of the notches will be determined by the size of the chip tobe formed, and its probable ultimate volume.

From the foregoing, it will be appreciated that it is an object of myinvention to provide an improved set screw. It is another object of myinvention to provide an improved set screw requiring, as far aspossible, no large increase in the force required to set it tight, butwhich will require a definitely increased amount of force initially toloosen it. It is a further object of my invention to provide an improvedset screw which, through the formation of a chip which must be disposedof in order to loosen the screw, and through the concurrent retention ofthe frictional locking of conventional screws in as large a measure aspossible, will serve the conjoint ends of requiring maximum forces toloosen it while maintaining at the practicable minimum damage to thesurface to be engaged by the screw or increased danger of breakages.These and other objects and advantages of the invention will, however,hereinafter more fully appear.

In the accompanying drawings, in which one illustrative embodiment ofthe invention is shown for purposes of illustration:

Fig. 1 is a side view of a set screw embodying the invention in itsillustrative form.

Fig. 2 is an enlarged fragmentary View showing the work engaging end ofthe set screw in side elevation.

Fig. 3 is a front end View of the set screw, also on an enlarged scale.

Fig. 4 yis a perspective viewof the front end of the set screw.

Fig, 5 is a central longitudinal sectional view of a bit-carrying chainblock, showing the set screw in a substantially, but not completely,tightened condition.

Referring to the drawings, and frstto Fig. 5, it will be observed thatthe lug portion i of a chain block 2, which is shown only in part, isprovided with a socket 3 in which a resharpenable type cutter bit il isshown in cutting position. An illustrative embodiment of my improved setscrew is shown at 5 threadedly engaged, by means of its own threadedportion 6, with an internally threaded bore 'i in the block, and withthe forwardmost work-engaging portion 8 thereof in Contact with theadjacent side of the bit 4.

ft will be observed that the forward end of the set 4screw is providedwith an externally frustoconical portion it and that this portion iscentrally countersunlr as at Il with the result that, before theformation of the notches later described, there exists an annularportion whose foremost edge or narrow surface, as may be desired (hereinshown as an edge l 2) lies throughout its circumference in a plane towhich the axis of the screw is perpendicular. The surface of thefrusto-conical portion I0 designated at I3 is adapted to have frictionalengagement with the seat which the set screw forms for itself` in thework when tightened; and this is also true of the surface lll whichbounds the depression formed by countersinking at l I.

The forward end of the 'portion of the screw is provided with, herein, apair of chip-forming,

' walls in addition, in some forms, to a bottom wall.

These notches may .be formed desirably by milling; and the forward wall,in terms of rotation in a tightening Vdirection of the screw, is slopingas at i6, the slope being so arranged that the notch is widest at its.mouth and the slope being further arranged desirably to cooperate inrolling down or rolling over the chip formedlas later described. Therearward wall of these notches shown at il is desirably substantiallyparallel to the axis of the screw. It will be observed, in View of thewidth or` space between the forwardmost portions of the walls IS and Il,that as the set screw is screwed inwardly there is what might be theannular extent of the mouth of the notch to 360, multiplied by the leadin linear measure of the screw. In other words, there is at I8 an edgehaving an effective projection, so far as the metal in advance of it, interms of its rotation in a screwing-.in direction is concerned,sufficient to raise a chip of a desired thickness. The width of thischip may be increased by changing from a line at I2 to a surface. Thethickness of the chip may be changed by varying the distance between theforwardmost points in the walls I6 and Il. The angle of the surface Ilwith respect to a plane including the axis of the screw may be varied,but satisfactory results are secured with the arrangement illustrated,namely, with the surface l'i parallel to a plane including the axis ofrotation of the screw. The depth of the notch may be varied, dependingupon the amount of chip which it is intended to form; and the angle ofthe surface i6 will be determined so Ias to roll down, rather than tobreak off the chip, if possible. There is no relief behind the surfacesIl, and hence a frictional binding effect between the surfaces i3 and laand the surfaces they engage will be provided, and the chips formed willbe of maximum strength and tenacity of connection with the body of themetal from which they are being raised.

It will be observed that the surfaces I6 and l1 are, in the illustrativeembodiment of the invention shown, separated at their innermost portionsby a surface i9, which is generally outwardly facing with respect jtothe notches, and forwardly facing with respect to'the set screw itself,`and slopes generally outwardly in a direction from the axis of thescrew towards its periphery. This surface, when engaged by a chip, willdeect the chip forwardly and cause it to roll, instead of resulting injamming as would occur in a sharp-cornered pocket. Ultimately, if andwhen the notch is lled with a chip, it will act to limit furthermovement of the set screw inwardly.

From the description which has been given, the mode of operation of the,invention will readily be seen. When the set vscrew is tightened, itforms a groove in the face of the piece to be gripped, most portions ofthe bottom wall of which lie in a single plane, but which has constantlyturned up two chips, with the illustrative construction, these chipsbeing received in the notches i5, I5 and rolled up in these notches andcompacted therein. When the screw has been tightened to theA desireddegree, it will be held -against release by the combination of twoactions. It cannot be released without getting the chips out of theway--either through breaking them off, or, as more ordinarily willoccur, rolling them down. The other action is the same action which ispresent with all conventional set screws of this type: a strongfrictional engagement between the surfaces i3 and i4 and the slopingside walls of the annular recess formed in the work.

I have found that to release my improved set screw to a point wherefitcan be freely unscrewed, many more foot pounds of force are requiredthan are necessary to release the conventional set screw, there being aprolonged resistance to unscrewing lasting through an angle of wrenchmovement of many degrees, whereas, when the conventional set screw isonce started the resistance falls off immediately to practicallynothing. t will be observed that, by reason of the nature of vmyinvention, damage (scoring) of the faces of the Shanks of the bits orholders is minimizedwhile yet, through the formation of the chips, adefinitely positive type of lock is provided. It will further be notedthat save for the relatively small arcuate gaps in the circular edge i2and faces i3 and te the frictional holding which is secured with aso-called standard type set screw is maintained. This is due in largepart to the absence of relief behind the surfaces l1 and portions I8.

Actual tests in use show that the danger of accidental loosening of myimproved set screw is far less than with a set screw not formed with thenotches l5, l5', since displacement ofthe chip in some manner isessential and since the forces tending to hold the set screw againstrelease are not immediately lost upon a very small angle of outwardturning of the screw.

While there is in this application specifically described one form whichthe invention may assume in practice, it will be understood that thisform of the same is shown for purposes of illustration, and that theinvention may be modified and embodied in various other forms withoutdeparting from its spirit or the scope of the appended claims` What Iclaim as new and desire to secure by Letters Patent is:

i. A set screw having at its end a projecting annular portionsubstantially V-shaped on radial planes and cut away at at least onepoint to provide a notch having a forward bounding wall, in terms oftightening rotation of the screw, sloping inwardly and rearwardly, andhaving an opposite wall having the elements of the surface thereof morenearly parallel to the aXs of the screw, said projecting portion, wherenot cut away as above mentioned, having the foremost points thereinlying substantially in a single plane perpendicular to the axis of thescrew.

2. A set screw having at the forward end thereof projecting arcuateportions adapted to be forced into the work to be held, upon tighteningof the screw, said arcuate portions each exceeding 90 in arcuate extentand being spaced by chip receiving notches having relatively straightsurfaces for raising as the screw is turned in a chip and havingrelatively sloping surfaces for displacing the chip as the screw isturned out, the parts of said projecting portions supporting saidchip-raising surfaces formed without relief.

3. A set screw having at the forward end thereof an annular portionadapted to be forced into the work to be held, upon tightening of thescrew, said annular portion having at least two relatively smallsections thereof cut away to form chip receiving notches bounded attheir forlward sides, in terms of inward rotation of said set screw, bysurfaces whose outermost portions are the most advanced, and at theirrearward sides having surfaces at least substantially parallel to eachother and to a single diametric plane, said annular portion presentingat least one forwardly facing surface adapted to engage with the workwith a binding frictional action on tightening of the set screw and saidset screw having at least one other forwardly facing surface disposedoutwardly of said rst mentioned forwardly facing surface and adaptedthrough the compactng of a chip between it and the surface from whichsaid chip is raised to limit advance of said set screw.

ll. A set screw having at its end a projecting annular portionsubstantially V-shaped on radial planes and cut away at substantiallyopposite points therein to provide notches having forward boundingwalls, in terms of tightening rotation of the screw, sloping inwardlyand rearwardly, and having opposite walls having the elements of thesurfaces thereof substantially parallel to the axis of the screw, saidprojecting portion, where not cut away as above mentioned, having theforemost points therein lying substantially in a single planeperpendicular to the axis of the screw, the portion of said projectingportion not cut away substantially exceeding the cut away part thereof.

5. A set screw having at its work-engaging end an annular portionadapted to be forced into the `work to be held upon tightening of thescrew, said annular portion having at least one relatively small sectionthereof cut away to form a chip-receiving notch bounded at its forwardside, in terms of screw rotation in tightening direction, by a surfacewhose outermost portion is the most advanced, and at its rearward sidehaving a surface at least substantially parallel to a diametric plane,said notch also having a bottom surface arranged between said surfacesand lying substantially in a plane and facing towards the work-engagingend of the set screw and at all points therein separated, from the eX-treme forward end of said work-engaging end by a distance less than thewidth of said chipreceiving notch at its mouth, for limiting the depthof penetration of said annular portion into the work to be held.

6. A set screw having at its Work-engaging end an annular portionV-shaped in cross-section and adapted to be forced into the work to beheld upon tightening of the screw, said annular portion having at leastone relatively small section thereof cut away to form a chip-receivingnotch bounded at its forward side, in terms of screw rotation intightening direction, by a surface whose outermost portion is the mostadvanced, and at its rearward side having a surface at leastsubstantially parallel to a diametric plane, said rearward surfaceproviding a cutting edge terminating in a point ywhich is at the leadingend of an arcuate edge which at all points arcuate to the rear of saidpoint lies forwardly of a line of like radial disposition but of thehelix angle iof the set screw, said cutting edge operative as the screwis rotated in a tightening direction to raise a chip on thescrew-engaging face of the Work and the chip so raised being received inthe space provided by the notch, said notch also having a bottom surfacearranged between said surfaces and facing towards the work-engaging endof the set screw for coacting with a chip for limiting the depth ofpenetration of said annular portion into the work to be held, saidbottom surface separated at all points therein from the forward end ofsaid portion by a distance less than the distance between the mostwidely separated points in said rst and second mentioned surfaces.

'7. A set screw having at its work-engaging end a projecting annularportion substantially V-shaped in section on a radial plane and adaptedto be forced into the work to be held upon tightening of the screw, saidannular portion being cut away at at least one point to provide a notchhaving a forward bounding wall, in terms of tightening rotation of thescrew, sloping inwardly and rearwardly, and having an opposite rear wallthe elements of the surface of which are more nearly parallel to theaxis of the screw, and further having a bottom wall between said wallsfacing towards the work-engaging end of the set screw, said rear wallserving as the screw is 7 8 'rotated in tightening Adirection to raise achip on the face of the Work and said bottom Wall be- REFERENCES CITEDing S0 disposed as t0 deflect the Chip s0 raised The followinglefeIBnCBS are 0f IGCOid in the toward said forward sloping wall so thatthe file 0f this patenti chip is caused to coil in the space provided by5 i said notch and to 11 the notch from top to UNITED STATES PATENTSbottom whereby the chip limits the degree of Number Name Daft@penetration of said set screw, and said sloping 1,330,792 FICk Feb. 17,k1920 wall serving to displace the chip as the screw is 2,112,493 HOSkYlgM2112 29, 1938 turned out and such displacing of the chip tend` 102,245,525 DCely June 10, 1941 ing Vto resist loosening of the screw.

LEON E. SIMMONS.

